A number of different techniques are in commercial use and by means of which articles are manufactured using synthetic plastics materials.
The most common technique is that of injection moulding. Injection moulding is capable of producing intricate articles. Because of the high pressure which is required, an injection moulding machine must be of very substantial strength. Likewise, the moulds that are used must also be capable of withstanding high internal pressures.
A form of moulding which does not require such high pressure is known as compression moulding. In this method a shot of molten synthetic plastics material is fed into the cavity of a female mould part. A male mould part is then pressed into the female mould part, the volume of the cavity decreases and the synthetic plastics material is forced to take-up the shape of the space remaining between the two mould parts. The pressure generated in the cavity is lower than that used in injection moulding. The technique is widely used for products such as bottle caps where short cycle times and high production volumes are required. This technique is limited insofar as the shapes that it can produce are concerned. For example, it cannot make components with undercuts.
If a component is to have a constant cross section throughout then it can be extruded. Extrusion involves the use of a die through which the molten synthetic plastics material is forced. This technique can, of course, only be used where the article is of constant cross section throughout. It is thus used for producing tubes, strips and bars.
A further known technique is thermoforming. This technique involves placing a heated and hence softened sheet of synthetic plastics material between two moulds and then closing the moulds to conform the sheet to the shape of the moulds. In some versions of this technique vacuum is applied to the underside of the sheet to assist in drawing it down into the lower mould.
There is a need in the plastics industry for a technique which, whilst being able to mould all the shapes that can be achieved by injection moulding, has the ability quickly to produce articles in larger numbers and/or of larger size than injection moulding can.
Increasing use is being made in industry of ceramics, of sintered metal and of composite materials filled with carbon and glass fibres and the present invention seeks to provide a new method of producing components using these materials. Injection moulding is not a method that can be used with filled plastics as the fibres can block the so-called pin gates through which the material flows into the mould.
A current method of making components from ceramics uses an injection moulding procedure but this procedure can only make small components.